Safety fuel



Patented June 8, 1943 SAFETY FUEL Cecil Brown, Baton Rouge, La),assignor to Standard Oil Development Company, a corporation of DelawareClaims.

The present invention is directed to fuels for aircraft, known as safetyfuels. V

Safety fuels are characterized bya high flash point, a high octanenumber, good volatility and gum stability. For example, a good safetyfuel should have a Tag closed cup flash point of 100 F. or more, anoctane number of about 100, and a boiling range of about 300-400 F. Itshould have also the other characteristics of good aviation gasoline,such as a good gum stability and a good breakdown test. I

The desirability of using a safety fuel has long been apparent in theaviation industry. Thus far, however, the industry has, not universallyadopted any standard safety fuel, primarily because there has been noavailable source of supply of such fuels ata suitable price. v

It has hitherto been proposed to produce safety fuels by several methodssuch as the destructive hydrogenation of selected dlstillates or crudes,the extraction with sulfur dioxide of certain distillates or crudes, andthecatalytic cracking under selected conditions of such extracts Thefuels produced by the first method are rather high priced due to thelimited quantity of suitable raw materialsl The fuels produced by thelatter two methods have so low' an initial octane number and so low alead susceptibility that the amount of lead required to convert theminto100 octane fuels makes their cost well-nigh prohibitive.

I have now found that fuels having satisfactory characteristics forsafety fuels such as high initial octane number, high leadsusceptibility and suitable boiling range can be produced from C4iso-hydrocarbons. For example, the copolymerization of normal andisobutylene yields a heavy hydrocarbon fraction which, whenhydrogenated,

boils between about 300 and 385 F., has ahigh flash point and a highoctane number.

I have found that by cutting themixture of hydrocarbons produced by thereaction between an isoparafiln and an olefin, such as isobutane andnormal or isobutylene, at about 300 F., it is possible to produce aheavy fraction having a boiling range of from about 300 to 400 F. whichhas .a Tag closed cup flash in excess of 100 F., a high initial octanenumber, and a high lead susceptibflity. A particularly desirable safetyfuel, according to the present invention, is a blend of the lastmentioned heavy fraction of alkylation product with hydrogenatedtri-isobutylenes boil-, ing between about 330 and 380 F., with thelatter constituting from 10 to 50% of the blend. These types of fuelsare disclosed and claimed in No Drawing. Application December 7, 1938",

. SerialNo. 244,357

copending application Serial No." 457,947, filed July 22, 1942.

The basic materials for the safety fuels of the present invention areavailable in large quantities and the methods by which they areconverted into the desired safety fuels are not costly. -For example,practically all refinery gases resulting fromcracking processes ofvarious types contain substantial percentages of isobutylene and normalbutylenes which can be caused to co-polymerize by being'contacted withsulfuric acid of a strength ranging from -60 to 75% at a temperaturebetween about 175 and 250 F. This process is usually conducted with aview of producing dimer, and to this end it is customary to recycletrimer to thereaction chamber. As the result of the presentinventiomthis process can be car- 'ried out with a view of producing,the highest yield per pass of high boiling hydrocarbons,

whereby 'the efficiency of the method is increased. If desired, theprocess can be so controlled as to produce mainly trimer by allowing theconcentration of dimer to buildup in the reaction chamber.

There are large reservoirs of isobutane which can be utliized as sourcesof raw material for the second embodiment of the present invention. Thereaction between isobutane and the olefins of refinery gases proceedswith ease at normal room temperatures in the" presence of concentratedsulfuric acid. This reaction, which yields a product containing C5+hydrocarbons, can be made to yield a product boiling mainly within the,safety fuel range by recycling C5 Cshydrocarbons to the reaction zone.

The fuels of the present invention do not'per se have an octane numberof 100. The co-p'olymer of isobutylene and normal butylenes,Whenhydrogenated, has an octane number of about90 which can be broughtto 99.5 with 3 cc. of tetraethyl lead per gallon.- Likewise, the highboiling alkylation fraction, especially when'blended with about 40% ofhydrogenated triisobutylenefhas a clear octane number of abopt 90whichtcan be raised to 100 with 3 'cc. of tetraethyl lead.

per gallon. v

The safety-fuel ofthe present invention is preferably composed entirelyof the reaction product of an iSO-C4 hydrocarbon with a different C4hydrocarbon. It may be mentioned, however, that, when the fuel is analkylation product, it may be produced from isopentane or isohexane aswell as from isobutane. Likewise, olefins other than .thebutylenes maybe employed. In any 'case, the fuel, as-previously men tioned, maycontain substantial quantities of hydrogenated triisobutylene. Othersuitable blending agents are alkylated aromatics boiling between.300 and400 F. Typical examples of such alkylated aromatics are ethyl benzene,propyl benzene,- isopropyl benzene, methyl ethyl benzene, o, m, p,trimethyl benzene, 1, 2, 3, trimethyl benzene 1, 2, 4, trimethyl benzene1, 3 5, secondary butyl benzene, isobutyl benzene, tertiary butylbenzene, and methyl isopropyl hen-- zene, p.

Alternatively, a fraction boiling between 300 and 400 F. of the productresulting from the alkylation of aromatics with olefins may, beemployed.

The characteristics of' typical examples of aviation safety fuelaccording to the present invention are given in the following table.Fuel A of this table was prepared by reacting isobutylene and normalbutylene in the presence of sulfuric acid of a strength of about 70% ata temperature of 170 F., recovering from the product a fraction boilingabove 300 F. and hydrogenating this fraction by contacting it with acatalyst composed of M003, ZnO and MgO at a temperature of SOD-600 F.and under a pressure of 3000 pounds per square inch in the presence of alarge excess of hydrogen.

Fuel B was prepared by reacting isobutane and the isoand normal butylenein C4 reflnery cut in the presence of sulfuric acid having a strength of98% at a temperature of 70 F. and under a pressure sufficient tomaintain the reactants in the liquid state and recovering from theproduct a fraction having the boiling range shown in the table.

.Fuel C was prepared by blending with fuel B hydrogenated triisobutyleneboiling between 330 and 358 F., the latter constituting 40% of theblend,

Fuel A Fuel B Fuel A. P. I. gravi 52 7 55.8 55. 8 Color Saybolt +19 +26+27 Aniline point. F 182 189 Sulfur .percen t.. 0. 01 0. 02 0. 008Doctor.-. Passes Passes Passes Corrosion cu. dish.. Passes Passes Passesish, m s 3.6 3. 8 Acid heat... 2 1 2 Bromine No.- 3 1 2 Flash .Tagclosed cup.. 112 1 Reid vapor pressure Below is! Below 1! Below 1;! Armyoctane number 89. 4 77. 0 85. 3 DtO. +3.0 cc. TEL 99. 5 96. 4 100Initial F 304 323 328 319 336 336 324 341 340 336 351 347 345 357 352352 363 355 362 373 361 Final F 384 393 385 Recovery .pcrcent. 98. 0 98.0 98. 0 Residue .do 1.0 l. 0 l. 0

.The nature and objects of the present invention having thus beendescribed, what is claimed as new and useful and is desired to besecured by Letters Patent is:

1. A safety fuel boiling substantially completely between about 300 and400 F., having a flash point of at least 100 F. by'the closed cupmethod, composed predominantly of the parafiinic compounds formed by thereaction between isobutane and a C4 olefin and contain- 2. A safety fuelboiling substantially completely between about 300 and 400 F.,having aflash point of at least 100 F. by the closed cup method, composedpredominantly of the paraflinic compounds formed by the reaction betweenisobutane and isobutylene, and containing sufficient antiknock agent tobring its octane number to about 100.

the closed cup method composed predominantly of saturated branched chainhydrocarbons of a the above stated boiling range which are separatedfrom the products produced by reacting isopentane and at least onemono-olefin under alflkylating. conditions in the presence of analkylation catalyst.

5. A safety fuel according to claim 4 in which sufficient: anti-knockagent is added to raise the octane number to about 100.

6. A safety fuel boiling substantially com-' pletely between about 300and about 400 F. having a flash point of at least 100 F. by the closedcup method composed predominantly of saturated branched chainhydrocarbons of the herein stated boiling range and which'are separatedfrom the product produced by reacting isopentane and at least one C4olefin under alkylating conditions in the presence of an alkylationcatalyst.

7. A safety fuel boiling substantially completely between about 300 andabout 400 F. having a flash point of at least 100 F. by the closed our:method composed predominantly of sat- -urated branched chainhydrocarbons of the herein specified boiling range and which areseparated from the product produced by reacting isopentane andisobutylene under alkylatlng conditions in the presence of an alkylationcatalyst.

8. A safety fuel according to claim 7 in which sumcient anti-knock agentis added to raise the ing suflicient antiknock agent to bring its octanenumber to about 100,

octane number to about 100.

9. A safety fuel boiling substantially completely between about 300 F.and about 400 F., having a flash point'of at least F. by

the closed cup method, composed predominantlyof paraflinic reactionproducts of an isoparaffln taken from the groupconsisting of isobutaneand isopentane and an olefin and containing sufllcient antiknock agentto bring the octane number to about 100.

10. A safety fuel boiling substantially completely between about 300 F.and about 400 F.. having a flash point of at least 100 F. by the closedcup method, composed predominantly of parafllnic reaction products of anisoparamn taken from the group consisting of isobutane and isopentaneand at least one butene and containing suflicient antiknock agent tobring the octane number to about 100.

L. BROWN.

